The present invention relates to a discharge lamp operating apparatus. In particular, the present invention relates to a discharge lamp operating apparatus for turning on and dimming a fluorescent lamp.
Fluorescent lamps are characterized by high efficiency and long lifetime, compared with incandescent lamps, and therefore widely used, especially for household illumination. In particular, compact self-ballasted fluorescent lamps are widely noted and spread because of their immediate substitutability for incandescent lamps.
In recent years, there has been a need for dimming fluorescent lamps in the same manner as in incandescent lamps. To meet this need, fluorescent lamps that can be dimmed are under development. In the case of incandescent lamps, which are not discharge lamps, the lamps can be dimmed comparatively easily by controlling the lamp power. On the other hand, in the case of fluorescent lamps, which are discharge lamps, dimming is not achieved satisfactorily simply by controlling the lamp power. Therefore, to dim fluorescent lamps, a phase-controlled AC voltage is input, and a lamp operating circuit is required to allow lighting with dimming.
FIG. 11 shows a circuit configuration of a conventional discharge lamp operating apparatus that allows lighting with dimming. The lamp operating apparatus shown in FIG. 11 includes a discharge lamp 12 and a driving circuit 26. The driving circuit 26 includes a DC power 4 and a DC/AC converting circuit 10, and a control circuit 16.
The DC power 4 rectifies a commercial AC power 1 with a diode bridge 2, smoothes the current with a smoothing capacitor 3, and outputs a DC voltage. The DC power 4 is connected in parallel to a series circuit of power MOSFETs 5 and 6, which are main switching elements. A LC resonance circuit including the discharge lamp 12, an inductor 7 for resonance, a capacitor 8 for resonance, a capacitor 9 for resonance and preheating current conduction is connected between the drain terminal and the source terminal of the power MOSFET 6.
The DC/AC converting circuit 10 is constituted by the power MOSFETs 5 and 6, the inductor 7 for resonance, the capacitor 8 for resonance, the capacitor 9 for resonance and preheating current conduction. The control circuit 16 is constituted by a power source part including a resistor 13 for power source and a zener diode 14 that are connected to the DC power 4, and a control circuit part 15. The control circuit part 15 is connected to the power MOSFETs 5 and 6, and the power to be supplied to the discharge lamp 12 is varied by varying the oscillating frequency or the ON duty of these switching elements. The control circuit 16 including the control circuit part 15 varies and controls the power to be supplied to the discharge lamp 12 in response to an instruction signal for dimming. Thus, the luminous flux of the discharge lamp is controlled for dimming.
FIG. 12 is a graph schematically showing the dimming state of the discharge lamp operating apparatus. The horizontal axis in FIG. 12 shows a dimming instruction, and the vertical axis shows the luminous flux level of the discharge lamp that changes in response to the dimming instruction.
FIG. 12 indicates that dimming can be achieved by varying and controlling the lamp power (curve B) in response to the dimming instruction. However, when the dimming instruction is made on the side of low luminous flux dimming in order to reduce the luminous flux, there is a problem in that unstable discharge occurs. The reason why unstable discharge occurs seems to be as follows. In a low luminous flux dimming region, it is necessary to control the power to be supplied (lamp power) to be small, so that it is necessary to constrict the lamp current. However, this results in very high lamp voltage (curve A) at the same time, as shown in FIG. 12. Thus, when the lamp voltage is so high as to be beyond the operating limit of the circuit, the circuit operation becomes unstable and thus unstable discharge such as a luminous lamp flashing on and off occurs. As a result, a stable dimming operation cannot be achieved from a full lighting state to a lighting off state, and a region where unstable discharge occurs as shown by a hatched region in FIG. 12 is generated. In lighting in the region where unstable discharge occurs, the lamp may flicker or flash on and off. In some cases, malfunction such as damage of the circuit during a low luminous flux dimming operation may occur.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a discharge lamp operating apparatus that can realize stable dimming operation from a full lighting state to a lighting off state with a simple circuit configuration.
A discharge lamp operating apparatus of the present invention includes a discharge lamp and a driving circuit of the discharge lamp. The driving circuit can vary the power to be supplied to the discharge lamp and has a function to turn off the discharge lamp at a supplied power value above a supplied power value at which unstable discharge occurs in the discharge lamp.
In one embodiment, the driving circuit includes a DC power; a DC/AC converting circuit connected to the discharge lamp at its output terminal, including a switching element for converting an output from the DC power to alternating current; a control circuit for varying the oscillating frequency or the ON duty of the switching element, thereby varying and controlling the power to be supplied to the discharge lamp; a lamp characteristics detection circuit for detecting that the power supplied to the discharge lamp has reached a predetermined value; and a stop circuit for generating a signal for stopping an operation of the control circuit when the predetermined value is reached.
It is preferable that the lamp characteristics detection circuit includes a delay circuit for delaying an output signal for a predetermined time.
In one embodiment, the stop circuit generates a signal for stopping an operation of the control circuit while the stop circuit receives an output signal from the lamp characteristics detection.
In one embodiment, the discharge lamp operating apparatus is constituted as a compact self-ballasted fluorescent lamp.
In one embodiment, the driving circuit can vary the power to be supplied to the discharge lamp continuously or discretely, thereby dimming the discharge lamp continuously or discretely.
According to another aspect of the present invention, a discharge lamp operating apparatus includes a discharge lamp and a driving circuit of the discharge lamp. The driving circuit can vary the power to be supplied to the discharge lamp and has a function to turn off the discharge lamp at a supplied power value above a supplied power value at which unstable discharge occurs in the discharge lamp. The discharge lamp operating apparatus further comprises means for supplying the power for a dimming level of a full lighting state to the discharge lamp for a predetermined period of time, regardless of a dimming level of the discharge lamp operating apparatus.
In one embodiment, the driving circuit includes a DC power; a DC/AC converting circuit connected to the discharge lamp at its output terminal, including a switching element for converting an output from the DC power to alternating current; a control circuit for varying an oscillating frequency or an ON duty of the switching element, thereby varying and controlling the power to be supplied to the discharge lamp; a lamp characteristics detection circuit for detecting that the power supplied to the discharge lamp has reached a predetermined value; and a stop circuit for generating a signal for stopping an operation of the control circuit when the predetermined value is reached. The means for supplying the power for a full lighting state for a predetermined period of time includes a timer circuit that operates for a predetermined period of time in connection with a switch for turning on the AC power; and a full lighting dimming instruction signal generating part for generating a full lighting dimming instruction signal for setting a dimming level to a level for a full lighting state, in response to an output from the timer circuit and outputting the signal to the control circuit. The control circuit includes a function to process the full lighting dimming instruction signal from the full lighting dimming instruction signal generating part before a dimming instruction signal for varying and controlling the power to be supplied to the discharge lamp, whereby the power for the full lighting state is supplied to the discharge lamp.
According to the present invention, the power to be supplied to a discharge lamp can be varied. In addition, since the driving circuit has a function to turn off the discharge lamp at a supplied power value above the supplied power value at which unstable discharge occurs in the discharge lamp, the discharge lamp can turn off at a predetermined supplied power value, in addition to being dimmed by varying the power to be supplied to the discharge lamp. As a result, unstable discharge is prevented from occurring in the discharge lamp, so that stable dimming operation can be achieved from the full lighting state to the lighting off state. In the case where a lamp characteristics detection circuit included in the driving circuit has a delay circuit for delaying output signals for a predetermined time, a malfunction due to a high voltage pulse that occurs at the start of lighting of the discharge lamp can be prevented. In addition, when a stop circuit included in the driving circuit is a circuit for generating a signal for stopping the operation of the control circuit while output signals from the lamp characteristics detection circuit are input, the stop circuit can be realized with a simple configuration where a complicated circuit for storing a stop signal or a reset circuit is not required.
According to the present invention, the power to be supplied to the discharge lamp can be varied, and the driving circuit has a function to turn off the discharge lamp at a supplied power value above the supplied power value at which unstable discharge occurs in the discharge lamp. Thus, the present invention can provide a discharge lamp operating apparatus with a stable dimming operation without unstable discharge from the full lighting state to the lighting off stage.
Furthermore, in the case where the discharge lamp operating apparatus includes means for supplying the power for a dimming level of a full lighting state to the discharge lamp for a predetermined period of time, regardless of the dimming level of the discharge lamp operating apparatus, the discharge lamp operating apparatus easily can turn on the lamp again. In the case where the discharge lamp operating apparatus is constituted as a compact self-ballasted fluorescent lamp, it can be substituted for an incandescent lamp, so that the discharge lamp operating apparatus of the present invention can be applied in a wide range.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.